Momentarily, it appeared that Lewis' trial had come to an abrupt end, until Common Pleas Judge Jeffrey Minehart explained that the jury would have to decide if Lewis, 23, of North Philadelphia, was guilty of first-degree or second-degree murder. With the plea, third-degree murder was taken off the table.

The question before the panel of eight women and four men is of life and death.

If the stocky, bespectacled, high-school dropout is found guilty of first-degree murder, defined as a premeditated, willful and deliberate act, the jury could impose the death penalty on him or life in prison without parole.

The District Attorney's Office is seeking a death sentence.

But if the jury finds Lewis guilty of second-degree, a murder committed without premeditation during another crime, his sentence would be life in prison without parole.

Lewis also pleaded guilty to weapons and related charges.

Before a courtroom that at times overflowed with police officers, including Commissioner Charles Ramsey, and Cassidy's family - wife Judy, and children Katie, Colby and John sat in the front row - the prosecutor and defense attorney showed their cards during sobering opening arguments.

Assistant District Attorney Jennifer Selber said the trial would detail how Lewis evolved from a robber to a killer in fall 2007.

Between Sept. 18 through Oct. 31, when Cassidy, 54, was gunned down, Lewis pulled six armed robberies of pizza shops and Dunkin' Donuts locations.

During his first robbery of the Dunkin' Donuts at Broad Street and 66th Avenue in West Oak Lane, Lewis took the money and fled without hurting anyone, Selber said.

By his fifth robbery at Feltonville Pizza on Rising Sun Avenue on Oct. 25, Lewis pistol-whipped a man, dragged a woman by her hair, pointed his 9mm handgun at two children and fired a bullet into the ground, she said.

Less than a week later, while robbing the West Oak Lane doughnut shop again, Lewis stood at the counter waving the same gun.

At one point he turned, took two steps forward, took aim from three feet away and shot Cassidy in the head as the officer entered the store, Selber said.

"Ladies and gentlemen, this murder was captured on videotape," said Selber, who described Lewis' actions as calculated and premeditated.

Lewis had robbed a family and a city of "a great man," she said.

Defense attorney Michael Coard was candid and quick about telling the jury that his client had killed Cassidy. "A hero died at the hands of John Lewis," he said.

Still, he asserted that the slaying was not premeditated but was rather "a panicky reaction during a robbery that led to a tragic death."

He told the jurors that if they kept their anger, sadness and outrage in check and applied the law as instructed by the judge, they would find Lewis guilty of second-degree murder.